A jack is one of the commonly used tools in our daily life. It is used to reduce the force required to lift a load over a preset lift distance. Its operational principle is to force the input piston, having a smaller sectional area, to move with a smaller force. The movement of the smaller piston pushes the hydraulic oil into the output cylinder, thus driving the output piston, which has a larger sectional area to lift the load. In accordance with the Law of Conservation of Energy, the input piston travels a much larger distance than the output piston does. Thus, it is typically necessary to push the input piston repeatedly to lift the load to a certain distance. In this process, each pumping cycle against the input piston results in the same lift distance of the output piston. This is independent of the magnitude of the load. As a result, in any case of an idle load (i.e., no load), a light load, or a heavy load, it necessary to pump the jack repeatedly, with the load going up very slowly. This wastes both time and effort.
To solve this problem, hydraulic jacks have been proposed in which a blind hole is formed in the middle of the piston of the output cylinder. An oil pipe is inserted into this blind jack hole. In the case of an idle load, when the piston of the input cylinder is pumped or pressed, the hydraulic oil flows into the blind hole via the oil pipe, and pushes against the end face of the blind hole. This moves the piston up at a fast speed. In the case of a heavier load, part of the hydraulic oil goes up and opens a sequential valve leading into the output cylinder. The oil thus applies forces against the larger ring-type thrust surface of the piston, and lifts the load slowly together with the hydraulic oil that flows into the blind hole and applies forces against the end face of the blind hole. Since the blind hole has a smaller area to receive force, the lifting speed of the jack is very fast in the case of an idle load. Generally, the piston of the output cylinder reaches the weight after being pumped one or two times. On the other hand, in the case of a heavy load, since the whole sectional area of the piston of the output cylinder is taken as the thrust surface, the purpose of saving effort is also achieved, enabling the heavy load to be lifted with a low force.
However, it is found from practical application this type of hydraulic jack cannot meet the requirements as expected above. The reason is that when the hydraulic oil is pressed into the output cylinder via the oil pipe, the piston of the output cylinder goes up rapidly; the pressure in the ring-type cavity of the output cylinder goes down swiftly to suck hydraulic oil from the oil tank. However, since the piston moves relatively fast and the area of the ring-type cavity changes very quickly, the sucked hydraulic oil cannot fully fill up the ring type cavity, resulting in a phenomenon of inefficient oil suction. Since there exists some air in the ring-type cavity of the output cylinder, when the output cylinder starts to lift load, the load applies forces to the piston and makes the piston fall back a certain distance, thus reducing the speed of the load lift. Moreover, after many, repeated pumping cycles, the air held in the ring type cavity of the output cylinder flows into the input cylinder via the oil circuit, bringing about the same phenomenon of inefficient oil suction for the input cylinder. This reduces the lift distance of each pump press, and additionally, the lifting efficiency. In addition, this type of jack has also another disadvantage. Since the lifting force comes from the hydraulic oil flowing into the blind hole via the oil pipe and into the ring type cavity of the output cylinder via the one-way valve, the area of the blind hole and that of the ring type cavity changes with each pump. It is necessary to ensure a balance between the pressures from the hydraulic oil flowing into the ring type cavity and that flowing into the blind hole to achieve a steady movement of the output piston. Unfortunately, it is very difficult to accomplish such a result in a practical mass production process. As a result, when the controlled hydraulic oil enters the ring-type cavity and is locked, crack of the thin-wall oil pipe happens often due to excessively high pressure in the blind hole. This results in low yield of finished products for this type of jack and thus increases its production cost.
It is an object of the present invention to provide a speed regulation jack, which takes the size of the load as signal and automatically transfers between different lift speed levels, so that the lifting efficiency of the jack is increased.
It is also an object of the present invention to provide a speed regulation jack in which a limit unloading mechanism is set to prevent the piston rod from striking the cylinder top cover and possibly cracking it, so that the lifting efficiency of the jack is enhanced.
The invention concerns a speed regulation jack, which comprises at least one input cylinder and one output cylinder, and hydraulic lines connected in parallel between the input and output cylinders. A differential oil circuit is connected between the inlet cavity and the return cavity of the output cylinder, and a control valve is connected in series between the return cavity of the output cylinder and the oil tank. This control valve controls the return oil of the return cavity.
A one-way valve is set in the differential oil circuit, and the return cavity of the output cylinder is unidirectionally connected to inlet cavity via this one-way valve.
A limiting or unloading mechanism is set at the front-end of the return cavity of the output cylinder.
A return groove can be set on the mating surface between the front-end of the return cavity and the piston of the output cylinder. The return cavity is unidirectionally connected to the oil tank via a one-way valve. The core of the one-way valve is fixed to a pressure pin out of the bush of the one-way valve. One end of the pressure pin is seated in the return cavity to control the opening and closure of the one-way valve, to thereby create a limit unloading mechanism. In the case of idle operation, when the piston reaches its maximum distance, it reaches the pressure pin and opens the limit unloading mechanismxe2x80x94the hydraulic oil in the inlet cavity of the output cylinder returns into the oil tank via the return groove and sequential valve. This can be used to meet the requirements of inspection and test standard in the case of from idle operation to maximum oil return.
The one-way valve with a pressure pin of the limit unloading mechanism can share the same valve core with the control valve to form a composite control valve.
The control valve can be a sequential valve.
The hydraulic line can be a hydraulic speed regulation line.
Speed regulation cylinders can be set in the hydraulic speed regulation lines.
The hydraulic speed regulation lines comprise at least two hydraulic sub-lines connected in parallel. These hydraulic speed regulation lines take the load pressure of the output cylinder as its control signal to control the opening and closure of its hydraulic sub-lines or their combination at different speed levels.
Control valves are set in the hydraulic sub-lines that take the load pressure as their control signal to control the opening and closure of the hydraulic sub-lines.
The opening pressure of the control valves in the hydraulic sub-lines is set in sequence and opens in sequence with the increase of load.
Speed regulation cylinders can be set in the hydraulic sub-lines and the difference between the piston areas of the input and output cavities in the hydraulic sub-lines are set in sequence.
The hydraulic sub-line at the lowest speed level in the hydraulic speed regulation line can be directly connected to the input and output cylinders via a control valve.
A flexible restoring mechanism is set in the speed regulation cylinder, and the output cavity of the speed regulation cylinder is connected to the oil tank via a one-way valve.
The speed regulation cylinder can comprise oil cylinders of two different levels, the sectional area of the first-level cylinder is less than that of the second-level cylinder, and the first-level piston and the second-level one are interconnected via a piston rod. Additionally, the speed regulation cylinder can also be made up of a single-level oil cylinder and its piston rod extends out of the input cavity.
The input cylinder, output cylinder and hydraulic speed regulation line can be set in one valve bush combination, and the output cylinder jacket is set in the oil tank.
The following illustrates the speed regulation operating method of the present invention in a mode where the hydraulic speed regulation line is made up of two hydraulic sub-lines. In the case of an idle load, when the piston of the input cylinder is pressed, the hydraulic oil is pumped to the input cavity of the speed regulation cylinder in the hydraulic sub-lines at a high speed level to push its piston to press the hydraulic oil in the output cylinder, and with the opening of the control valve, the hydraulic oil flows into the output cylinder and then pushes the piston of the output cylinder to move forward. Since in such a case the pressure in the return cavity of the output cylinder is not high enough to open the sequential valve connected to the oil tank, the sequential valve remains in its closed state. Thus, the hydraulic oil in the return cavity of the output cylinder flows into the inlet cavity of the output cylinder via the one-way valve to form a differential oil circuit that increases the lifting speed once again. In this case, the piston rod of the output cylinder lifts load at the first speed V1. When the piston in this input cylinder is raised, the piston in the speed regulation cylinder returns to its original position under the forces from the flexible restoring mechanism, and meanwhile, the output cavity connected to the oil tank sucks oil and fills up the output cavity. When the piston in the input cylinder is pressed once again, the above process repeats. In this process, since the sectional area of the piston in the input cavity of the speed regulation cylinder is smaller than that of the piston in the output cylinder, the lift distance to lift the load each time is increased via the differential oil circuit of the output cylinder, the lifting speed is enhanced. The lifting speed V1 is the fastest one.
With the gradual increase of load of the hydraulic jack, the pressure of the output cylinder is gradually increased. The pressure of the input cylinder is still not high enough to open the sequential valve in the low-speed hydraulic speed regulation sub-line. However, the pressure of the return cavity of the output cylinder becomes higher, opening the control valve connected to the oil tank. The hydraulic oil in the return cavity directly flows back into the return tank via this control valve. In such a case, the pressure of the inlet cavity of the output cylinder is higher than that of the return cavity and the one-way valve in the differential oil circuit is closed. With the differential oil circuit blocked, the piston rod of the output cylinder lifts load at the speed V2. Since in this case, there is no further speed regulation via the differential oil circuit, the speed V2 is less than the speed V1 (V2 less than V1). However, the capacity to lift load in this case is enhanced, being capable enough to lift the load.
With the further increase in the load of the hydraulic jack, the pressure of the output cylinder also increases further. The jack enters a heavy load state. In such a heavy load state, the pressure of the hydraulic oil produced from the output cylinder is higher than the set pressure of the sequential valve in the low-speed hydraulic sub-line, and thus the sequential valve opens. Part of the hydraulic oil in the input cylinder flows into the inlet cavity of the output cylinder via this sequential valve, and as a result, the piston rod of the output cylinder moves at the speed V3 to lift the load. Since there is no speed regulation cylinder set in the low-speed regulation sub-line, the speed V3 is less than the speed V2 (V3 less than V2). However, in accordance with the Law of Conservation of Energy, the capacity to lift the load increases under the same pressure, being capable enough to lift the load.
In the above operating process, the transfer between various lifting speeds is automatically done with the change of the load, and does not require any additional operation or control. The present invention not only enhances the lifting efficiency, but also features simple and easy operation, achieving the purpose of both time and effort savings. Besides, in the speed regulation process, except that the input cylinder absorbs oil as does a conventional jack when the low-speed hydraulic sub-line between the input cylinder and output cylinder of hydraulic sub-line opens, there is no oil added into the input cylinder at all the other speed levels. It only takes the hydraulic oil as a medium of pressure transfer to transfer the pressure applied against the piston of the input cylinder. As a result, it does not involve the problem of inadequate absorption of oil in the input cylinder, as is the case with the existing technology. Furthermore, the absorption process of oil after the input cylinder directly pumps hydraulic oil into the output cylinder via the low-speed hydraulic sub-line does not involve the problem of inadequate absorption of oil. All of the above works to avoid the phenomenon of falling back during lifting and thus ensures the work efficiency of lifting load.
Besides, in the present utility model, since there is a limit unloading mechanism set at the front-end of the oil return cavity, when the piston of the output cylinder reaches its maximum distance, the limit unloading mechanism opens and starts to relieve load, thus avoiding the phenomenon that the piston strikes the end cover of the cylinder when the jack reaches its maximum lifting position. Furthermore, since the limit unloading mechanism is formed by the return groove on the mating surface between the front-end of the return cavity in the output cylinder and the piston and the one-way valve with a pressure pin, when the piston in the output cylinder reaches the front-end of the return cavity, the inlet cavity of the output cylinder is connected to the return cavity via the return groove. Meanwhile, the piston holds against the pressure pin fixed to the valve core and opens the one-way valve. The hydraulic oil in the inlet cavity flows into the return cavity via the return groove, and then into the return tank via the one-way valve. In such a case, no matter how the operator applies force to press the piston rod of the input cylinder, the piston of the output cylinder remains static without any lifting operations since the pressure of the inlet cavity and that of the return cavity are balanced. As a result, this avoids the phenomenon that the piston strikes and possibly cracks the end cover of the cylinder. Additionally, since the hydraulic oil of the inlet cavity of the output cylinder can flow back into the return tank via the return groove in the first place and then via the one-way valve connected to the oil tank, then the inlet cavity does not involve the phenomenon of overload relief. As a result, the load, which has been lifted to a position, will be kept there without falling down as a result of the unloading.
In the jack in the present invention, three or more hydraulic speed regulation sub-lines can be connected in parallel. With one hydraulic sub-line added, two speed levels are accordingly added. This makes the jack""s speed adjustable between multi-levels during its operation. In terms of its design, different specifications of the jack can be worked out according the magnitude of the load so that in application, different jacks of different specifications can be selected depending on the specific requirements. When it is used to lift relatively smaller load, a jack with relatively fewer speed levels can be selected. On the other hand, when it is used to lift a relatively larger load, a jack with relatively more speed levels can be selected. Since the jack of the present invention exhibits different lifting capacities when it is working at different speed levels, it is, in fact, equivalent to a conventional jack with a corresponding lifting capacity. The effect when it is working at different speed levels in parallel is equivalent to several jacks of different specifications working at different load ranges with the increase of the load when it is used to lift load. As a result, the present invention incorporates functions of several conventional jacks of different specifications into one jack, and automatically regulates its speed in correspondence with the load changes. It is simple and convenient in lifting operations with enhanced lifting efficiency and equipment utilization rate.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.